Orchid Wise

Cymbidium Pests & Virus

Cymbidium Pests and Virus

We are really fortunate that Cymbidiums are relatively tough plants, with not a lot of pest and disease problems.  You might not agree, if you have a plant, which suffers regularly though.  Some varieties give more problems than others, but generally, most are not prone to giving us many problems. 

The list below is what one most needs to be watchful for.  It is not a complete list, but if you can eliminate, or control them, you are likely to be successful:

Scale

Scale is a little conical shaped insect which attaches to the leaves & sucks nutrition from the leaves.  Each insect is about one millimetre in diameter, but they breed rapidly and often are first seen in large numbers, often on the underside of the leaves.

They need to be treated as soon as they are discovered, or they will multiply quickly.  Preventative spraying is most commonly used.  Confidor, Eco Oil or Mavric and others, are worth trying.  Foliar spraying is effective, but drenching the pot with a systemic insecticide can be more effective.

They can be carefully wiped off using a tissue or cloth, or rubbed with a cotton wool bud dipped in methylated spirits, or suitable insecticide, and also hosed off using a high pressure water jet.

Predators can be very successful in controlling them.  One good natural predator is small wasp called Aphytis melinus, available from Biological Control Services, at Loxton, SA. (www.biologicalservices.com.au).

Scale discolours the leaf where they are attached, and it often takes many months before the spots they cause, disappear.  Marked leaves make the plant unattractive, and reduces the chance of winning a prize.

Some varieties are more prone to being infected with scale.  Most of the Sarah Jeans, and many of their progeny, are regularly attacked by scale.  It is possible to use the Sarah Jeans, as an indicator plant, for the presence of scale in your collection.  Monitor the Sarah Jeans, and treat for scale at first signs, and you might just keep it under control.

Two Spotted Mite or Red Spider Mite

Very small mites, which live most of their lives on the underside of the leaves.  They are hard to spot and only about half a millimetre in size, and are a sap sucking insect.

They can quickly build up into large numbers due to a short reproductive cycle, and will then cause serious damage, by sucking on the leaf.  Badly damaged leaves take on a silvery colouration on the underside of the leaves.  A mature plant will not perform to its best if badly attacked by them.  Small plants will suffer very badly, and often die.

Spraying with a miticide will control this pest, but a series of sprayings is usually required.  Most sprays do not kill the eggs so a follow up sprays 5 to 7 days after an initial spraying is needed, to kill new hatchlings.  And I would repeat this again if you wanted to be sure.

There are many miticides available, but the following have been successfully used by many growers.  Kelthane, Omite, Sanmite, Mavrik.  Predators are also available to control this pest.  Biological Services have a predatory mite called Typhlodromus occidentalis which is effective in controlling them.

The use of foggers, to maintain a very humid environment, seems to control mite numbers, but will not eradicate them.

Mites are also a serious problem as you won’t even know they are there until it’s too late.  Tthey are readily spread by wind and are carriers for viruses that infect Cymbidiums, and once infected, plants must be destroyed.  Please be extra vigilant in relation to this pest, as it is one of the causes of complete collections being infected and needing to be destroyed.  Mine included!

Slugs and snails

Slugs and snails can cause major damage to buds and flowers, and cause great disappointment, when they damage a potential show winner. Many growers, tend to just concentrate on control, during the wet weather periods, when they are active, coinciding with the cymbidium flowering time.  If one applies preventative practices all year, numbers are less likely to build up and cause problems.

There are several safe ways to minimise slug and snail attacks, but usually baiting with special baits is required.  Spraying the growing area with coffee is effective too.  Sharp sand, or crushed egg shells, can make it difficult for a slug or snail to slither towards your prize plant.

Baiting with one of 3 common chemically based baits is the most common form of control. Many growers are fearful of dogs and cats, eating the baits so be careful with pets.  There is iron chelate based bait available, which is relatively safe for pets, and is very effective.  The old metaldehyde based bait (often green coloured), is effective, but is quickly reduced in effectiveness if wet.  The newer, blue coloured baits (Baysol), are more effective in wet conditions.  There is a sprayable product available. Measurol is a powder, which can be mixed in water and sprayed over the plant foliage and benches to give good protection.

Generally some form of regular baiting is necessary to prevent buds and flowers being damaged by slugs and snails if they are prevalent in your area.

Caterpillars

Caterpillars are always a danger to buds and flowers. There is always the occasional grub, which will just appear and chew on your future champion flower. Often there are early signs of their presence, in the form of their droppings, usually very small black pellets. Keep an eye out for them, and search the area around the droppings. Many of these grubs are green, making them difficult to find. Check in the sheath of the flower spike. Many a small grub will set up home in there, eating the flower spike, under cover of the sheath. Remove the sheath as soon as practical, to make your plant less welcoming to this little pest.

Many areas are inhabited by a hairy caterpillar, we call the “woolly bear”. It is interesting; some areas are infested badly with them. Other areas, often quite close, rarely see them. I suspect they are dependent on several food sources, perhaps not common in some areas, common in others.

The best protection from these quite migratory pests is to keep the areas around your growing area clean and free from weeds. Regular monitoring of adjoining areas, might locate sources of them, which can be treated. I have suffered often, particularly when growing in suburban areas. Caterpillars can move at astonishing speeds, from neighbouring properties. An occasional old spike of flowers, on the floor, will often snare a new visitor to your growing area. Monitor it regularly, and dispose of pests attacking the old flowers. Spraying with Mavrik is a good prevention. Dipel is a biological control, which works well, but needs regular application, because it washes off easily.

The use of an insect zapper is useful to attract and destroy moths which lay the eggs, which later hatch into grubs, and attack your flowers. The moth which are parents to the woolly bear, become airborne in late January, through February, in Adelaide. A bug zapper, employed at that time, will eliminate hundreds of moths and helps minimises the woolly bear populations later in the season.

Rats and mice

Rats and mice are common in many areas, and will attack orchid plants and the flowers.  Rodents can get a taste for the pollen in the flowers & will easily scale the flower spike to access this delicacy.  They will also eat new flower spikes and even whole green bulbs.  In suburban areas, there is often seasonal fruit falling from trees and rats particularly feed heartily on fallen fruit, and when it is no longer available they look for other food sources.  They will happily completely eat out the green bulbs of selected cymbidiums.  Continual baiting minimises this problem.  Again, dogs and cats can fall foul of baits so be careful.  We make a bait station, from a piece of small diameter stormwater pipe so pets cannot access it, and ensure it is stocked year round.  There are also many traps which could be utilised if you suspect you have rodents.  Watch out for plant labels mysteriously being removed from their pots.  Rats will remove labels for use as a nesting material, but often drop it before reaching the nest.  We suggest you should have rat and mice baits out, year round.  If you do, you are unlikely to have problems in this area.

In rural areas, rabbits also love to visit and eat big numbers of small orchid plants.  They seem to have a special liking for any Sarah Jean varieties!  So rabbit proof your growing area.

Orchid Virus

Orchid Virus is a huge problem for all of us.  If the grower is not careful and practice sanitary prevention procedures.  Orchid virus is like many common viruses, in that it is easily spread if care is not taken, but can be generally and easily prevented from spreading by following one simple rule.

Ensure that no fluid from one plant is transferred to another plant.

Assume every plant in your collection has virus (it probably doesn’t), and don’t contaminate one plant with sap from another plant. It is very much like we teach our children, to prevent the spread of disease in humans.  The most common way to spread virus is with cutting instruments, or the re-use of pots, from another plant.  Many unsuspecting or unknowing growers cut a plant with a pair of cutters, then use them to cut another plant without sterilising it.  If using this practice, it is likely that at least one of your plants has virus, and you will quickly spread it to many other plants in your collection.

Many collections are started from gifts of old plants, from relatives or friends, who know nothing about orchid virus, or its prevention.

Advanced Orchid Fleck Virus

Many old plants have virus, but show little signs of it, or the grower is unable to see the signs of virus in their plants.  And in some cases many growers are happy to grow plants which have virus as they can’t bear to lose the plants they have.  

They might show little signs of the virus for a long time.  They can flower and grow quite normally.  Put them under stress and they often deteriorate, and eventually die.  All this time, they can potentially infect your whole collection.  Virus shows up as leaf markings.  Ask at your orchid club to be shown photographs, or actual infected plants.  There is also lots of information on the internet, including lots of photographs.  Google orchid virus and you will get huge amounts of information.  

There are three common viruses in cymbidiums – Cymbidium Mosaic Virus (CymMV), Odontoglossum Ringspot Virus (ORSV) and Orchid Fleck Virus (OFV). Each of these is covered in detail in our article on Cymbidium virus.  There is no cheap way of ridding an infected plant of virus.  Serious growers isolate a suspect plant from their collection, and monitor it carefully (or discard it immediately).  There are other causes of leaf markings which look like orchid virus, such as poor fertigation, which often disappears, after improved fertilising.  

The only sure way to be sure if a plant has virus, is to have have it tested.  The Department of Agriculture in Hobart will test a sample of leaf, for about $30.  There is also a simple test kit available which is a really good, quick, easy and reliable way to test your plants for Cymbidium Mosaic Virus (CymMV) and Odontoglossum Ringspot Virus (ORSV).

Some orchid clubs and commercial growers have the kits available.  Cost is usually between $8.00 and $12.00, and each kit tests just one plant.  Overseas it is common for serious growers to test each plant in their collection, and then test each new plant, before allowing it in to the collection.

Generally, many growers are not careful enough with virus awareness in their collections, and need to improve their knowledge and seriously adhere to safe, virus preventative methods.

Sterilise cutting tools by flaming them, or soaking in a saturated solution of Tri Sodium Phosphate, for at least 20 minutes. Have lots of cutting tools available.  Many orchid clubs sell Tri Sodium Phosphate on their trading table.  If not, get the club to make it available. It is important to use it.

Please refer to our extensive article on Cymbidium viruses here for more information, photographs and explanations.

Bulb Rot

Bulb rot in plants can be a major problem, and unless monitored often, can be the cause the loss of many plants, quickly.  It seems to be more prevalent in recent years, suggesting that there might be a new form of fungus or bacteria which attacks our cymbidiums.  

It can show up in various ways.  The yellowing or browning of the central leaves on a new growth must be watched.  These leaves can be easily pulled off the plant, and this action often allows air into the affected bulb, and the infection may clear up.  However, the bulb may become soft, even quite rotten, and when squeezed, ooze liquid. 

Prompt action is then required. It might present with all the leaves on a mature bulb going yellow and dying, and the bulb going rotten. Sometimes the bulb develops black marks and takes on a glazed look.  The plant needs serious remedial work, and quickly needs isolation from the collection to protect other plants.  Orchid growers are still experimenting to find the best way to minimise this problem.

It is quite contagious and adjacent plants, and that area, need watching and treating with various fungicides.  Copper Sulphate, 40 grams per litre of water, is a good sterilant for the growing area, but don’t put it on the plants.  Cymbidiums don’t like copper at that concentration.

The plant should be removed from the pot, and the infected bulb or bulbs cut off.  Often a dark area can be seen in the cut area.  This is an indication that the next bulb might also be infected, and might need removal.  Often the root system has died, and many roots are soft and squishy, not firm and crisp.  The potting mix is often very wet, indicating that the plant is no longer extracting moisture from it.  Serious root removal is required.  The plant might benefit from a thorough drenching with a fungicide.  Many plants will not recover.  We find that some recover, but repeat the rot process the following year.

The rot problem seems to affect some varieties more than others.  Some varieties have a high incidence of it.  Others are rarely affected.

There are suggestions that growing plants on benches, not on the ground will prevent it.  That is not so, with many growers using benches, having rot problems.

We had plants tested by SARDI, our agricultural research laboratory.  They informed us that our rot is actually a bacterial infection, but the bacteria enter the plant after a fungus attack.  Prevention is the best defence.  Spray regularly with a series of fungicides, particularly during warm and wet weather conditions.  We get most problems after rain during spring and autumn.  Growers here who have mastered it have put a fungus spraying program in place, and use different fungicides each time they spray.  The rot problem can be mastered, but it must be closely monitored and preventative spraying practiced.

Orchid Wise Society

With over 30 years of experience joining the Orchid Wise Society is a great way to join other cymbidium orchid grower enthusiasts around the world. I promise not to overload your inbox with unnecessary rubbish, instead I pride myself on providing relevant & interesting information with regards to all things Cymbidium orchids. 

I welcome your feedback on past newsletters and suggestions for what you would like to see in future ones. 

Thanks,

Karl

Join Orchid Society to learn more about Cymbidium Orchids
Scroll to Top